In overhead camshaft systems including a variable valve timing mechanism, a cam cover or cam journal cap may be included at an axial end of the camshafts to retain the camshafts and regulate oil flow to the variable valve timing mechanism. For example, U.S. Pat. No. 6,186,105 to Yonezawa discloses a cam journal cap that houses a control valve which controls oil flow to a variable valve timing mechanism. Specifically, the control valve receives oil from the engine oil system, and directs the oil to advance and/or retard chambers of a camshaft phaser to adjust the timing (e.g., phase angle) of the camshaft relative to a driving element of the camshaft such as a crankshaft.
To restrict translational movement of the camshafts relative to the engine cylinder head and cam journal cap, the camshafts may include a flange, which may be commonly referred to as a thrust ring, that is received in a groove or bearing surface of the cam journal cap. However, as the camshafts rotate relative to the cylinder head and journal cap, the thrust ring and thrust bearing may require sufficient lubrication. Thus, oil may be routed to the thrust bearing for lubrication thereof. However, an oil circuit dedicated specifically to the thrust bearing may be costly and may increase packaging size of the engine system. Specifically, more oil and a larger oil pump may be required in systems where the thrust bearing has its own dedicated oil circuit.
Some attempts to address the material and energy costs associated with lubricating a thrust bearing include utilizing a portion of the oil supplied to the variable valve timing mechanism to lubricate the thrust bearing. One example approach is shown by Lunsford et al. in U.S. Pat. No. 7,942,121, where oil provided to the variable valve timing mechanism may be returned to the control valve, and then directed to a groove in the cylinder head which receives the thrust ring. Therein, oil used by the variable valve timing mechanism may be drained from the control valve to the thrust bearing for lubrication thereof.
However, the inventors herein have recognized potential issues with such systems. Specifically, oil flow to the control valve may be highly variable depending on engine operating conditions such as engine speed and load, oil temperature, and the oil budget of the engine system. Thus, as the amount of oil provided to the control valve varies, so too does the amount of oil directed to the thrust bearing. As such, in systems where oil provided to the thrust bearing is sourced from the control valve, lubrication of the thrust bearing may be inconsistent. Further, in systems where the thrust bearing is retained by the overhead cam journal cap, and thus lack a pocket in the cylinder head to retain oil, lubrication of the thrust bearing may be interrupted during low levels of oil flow to the control valve.
As one example, the issues described above may be addressed by a cam journal cap comprising a thrust bearing coupled to a camshaft, a vertical bore housing a control valve, the control valve regulating oil received from an oil pump to control a position of the camshaft, a port positioned in the vertical bore and coupled to the thrust bearing to supply oil thereto, and a drain port positioned in the vertical bore above the port and coupled to an oil sump.
The vertical bore in some examples may form a housing for the control valve, and the control valve may include a spool, movable within the control valve's body for adjusting oil flow through the valve. However, each of the port and the drain port may be positioned within the vertical bore vertically below a bottom end of the spool and body of the control valve. Further, the port and drain port may be hydraulically in parallel, so that oil may flow out of both the port and drain port when oil levels in the valve exceed a threshold. Otherwise, oil may flow out of the port and not the drain port.
In another example, a cam journal cap may comprise a thrust bearing for receiving a thrust ring of a camshaft, and a vertical bore configured to house a control valve for a variable camshaft timing (VCT) system, said vertical bore including a first port for receiving oil from an oil pump, a second port for flowing oil to an advance chamber of the VCT system, a third port for flowing oil to a retard chamber of the VCT system, a fourth port, coupled to the bearing for flowing oil thereto, and a drain port for flowing oil to an oil sump.
In this way, consistency of oil flow to a thrust bearing may be increased, and the size and cost of an engine oil system may be reduced. By providing oil to the thrust bearing from an oil control valve of a variable cam timing system, an amount of oil in the engine oil system, and therefore the size of a pump of the oil system may be reduced. Further, by providing a vertical bore in the cam journal cap which houses the control valve, inherent oil leakage of the control valve may be collected at the bottom of the vertical bore. Oil collected at the bottom of the vertical bore may then be used to lubricate the thrust bearing. Further, oil levels in the vertical bore may be kept to within a desired range by draining excess oil through a drain port in the vertical bore when oil levels in the vertical bore exceed a threshold. In this way, oil levels in the bottom of the vertical bore may be kept at high enough levels to provide consistent oil flow to the thrust bearing for lubrication thereof. However, oil levels may be kept below levels which would inhibit operation of the control valve.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.